1. Technical Field
The present invention relates to an electro-optical device such as a liquid crystal device, to a method of manufacturing the same, and to an electronic apparatus equipped with the electro-optical device such as a liquid crystal projector.
2. Related Art
In this type of electro-optical device, electro-optical material such as liquid crystal, etc., is inserted between a pair of substrates. A plurality of pixel electrodes are provided on an element substrate which is one of the substrates. Also, counter electrodes facing the plurality of pixel electrodes are provided on a counter substrate, which is the other one of the substrates. Moreover, peripheral circuits such as a data line driving circuit, and a scanning line driving circuit, which drive pixel electrodes etc., are provided on the element substrate, and a plurality of wiring lines are led from a plurality of external circuit connection terminals to the peripheral circuit. The electro-optical device thus constituted is set, at the time of completion or delivery thereof, to an inspection device to which a power signal, a test image signal, etc., are supplied, and then its operation is inspected or adjusted.
After the inspection or adjustment of its operation is complete and the electro-optical device is removed from the inspection device, electrical charges based on various signals remain on the peripheral circuit or the wiring lines of the electro-optical device. In particular, if electrical charges by the image signals or the counter electrode potential remain on the image signal lines or the counter electrode potential lines, a DC voltage is applied between a pixel electrode and a counter electrode, and thus the liquid crystal, etc., located between both electrodes are burned in. Alternatively, if the electrical charges remain as described above, it is difficult to perform an inspection or adjustment again afterwards with a high precision.
Based on this contemplation, Japanese Patent No. 3173200 proposes a technology that connects, outside the electro-optical device, external circuit connection terminals connected to image signal lines and external circuit connection terminals connected to counter electrode potential lines respectively via resistors or short-circuit switches. Also, Japanese Patent No. 3240829 proposes a technology that connects, inside the electro-optical device, the entire wiring lines to ground potential lines, etc., via internal resistor lines that are formed of a semiconductor layer constituting pixel switching thin film transistors (hereinafter, referred to as “TFTs”). Either of the technologies enables the removal of the residual charges in the electro-optical device as described above.
However, according to the technology disclosed in Japanese Patent No. 3173200, the terminals to which the image signal lines are connected are connected to the terminals to which the ground potential lines are connected in a terminal-to-terminal manner. Accordingly, resistors or short-circuit switches for connection purpose are required to be provided outside the electro-optical device. Moreover, in fabricating the resistors or short-circuit switches for connection purpose by using the technology, it is difficult to secure an area for fabricating such resistors or short-circuit switches in the limited area on the substrate. In particular, in case of a small-sized electro-optical device or an electro-optical device having a large image display region in view of the substrate, it is extremely difficult to secure such area. Moreover, if the discharge resistors are fabricated in a small area at a region on the substrate, in other words, small-sized discharge resistors are fabricated, the possibility that the small-sized discharge resistors are destroyed by an electrostatic breakdown due to static electricity becomes higher. In particular, when other wiring lines are placed on an upper or lower layer of the small-sized discharge resistors via an interlayer insulating film, a capacitor structure is constructed via the interlayer insulating film, and thus the possibility that the discharge resistors at this portion are destroyed by an electrostatic breakdown becomes extremely high. In sum, fabricating resistors or short-circuit switches inside the electro-optical device as disclosed in Japanese Patent No. 3240829 makes the substrate or the overall device larger, or alternatively, makes the device deteriorated due to static electricity, and thus substantially disadvantageous in practice.
On the other hand, according to the technology disclosed in Japanese Patent No. 3240829, the discharge resistors are formed of the film used for thin transistors, and thus the degree of design freedom is excessively low. Therefore, fabricating the discharge resistors having appropriate high resistances in the limited area on the substrate, or fabricating the discharge resistors having appropriate high resistances in a small area, is difficult or, practically impossible. In other words, from the relation of the performance, etc., that is required for the pixel switching thin film transistors, if the same film is used both for the pixel switching thin film transistors and for the discharge resistors, restriction on the resistance value, area, and location of the resistors that can be fabricated becomes excessively significant. Additionally, even with this technology, as with the technology of Japanese Patent No. 3173200, using small-sized discharge resistors would increase the possibility of an electrostatic breakdown.